DESCRIPTION: This application describes continuing studies on the temporal and spatial regulation of the bithorax complex. The bithorax complex controls the development of 9 parasegments in the posterior half of the fly. The three homeotic genes in the complex are expressed in an intricate, parasegment specific pattern which is generated by a large regulatory region of more than 300 kb. This parasegment specific pattern is activated during early development by transient molecular signals that mark poistion along the body axis. It is then maintained by a different mechanism, involving genes in the Polycomb Group, during remainder of the life cycle. In animals which are mutant for one of these Polycomb group genes, the bithorax genes are intially activated in an appropriate spatially restricted pattern, but their expression soon spreads throughout the anterior/posterior axis. Much of the investigator's effort over the past several years has been directed towards understanding how the Polycomb Group genes maintain appropriately restricted patterns of expression and how this is coupled to the initial activation of the homeotic genes in the early embryo.